I'm Steve Ember with the VOA Special English Development Report.

Health and climate scientists have mapped how climate change affects different parts of the world in different ways. The scientists point to evidence that changes in the past thirty years may already be affecting human health. Possible effects include more deaths from extreme heat or cold, from storms and from dry periods that lead to crop failures.

Temperature changes may also influence the spread of disease. For example, warmer weather speeds the growth of organisms that cause diseases like malaria and dengue fever.

The work by scientists from the University of Wisconsin-Madison and the World Health Organization appeared in the journal Nature. The W.H.O. is a United Nations agency.

The agency recently estimated that climate changes caused by human activity lead to more than one hundred fifty thousand deaths each year. Cases of sickness are estimated at five million. And the W.H.O. says the numbers could rise sharply by 2030.

Jonathan Patz of the Gaylord Nelson Institute for Environmental Studies at Wisconsin led the study. Professor Patz notes that climate scientists linked global warming to the heat that killed thousands in Europe in August of two thousand three. But he says poor countries least responsible for the warming are most at risk from the health effects of higher temperatures.

Professor Patz says areas at greatest risk include southern and eastern Africa and coastlines along the Pacific and Indian oceans. Also, large cities experience what scientists call a "heat island" effect that can intensify conditions.

Professor Patz says average temperatures worldwide have increased about one-third of a degree Celsius in the last thirty years. But he tells us even that can make a difference with a disease like malaria. The report says average temperatures could increase as much as six degrees Celsius by the end of the century.

Professor Patz says the world faces an important moral test.

Representatives from about two hundred nations have been meeting in Montreal, Canada, to discuss climate change. The ten-day conference ends December ninth. It is the first such United Nations meeting since the Kyoto Protocol took effect earlier this year. The treaty seeks to reduce the amount of carbon dioxide and other heat-trapping gases released as pollution into the air.

This VOA Special English Development Report was written by Jill Moss. Our reports are online at voaspecialenglish. I'm Steve Ember.